Walk into any bookstore or library, and you'll find shelves and shelves of hugely popular novels and book series for kids. But research shows that as young readers get older, they are not moving to more complex books. High-schoolers are reading books written for younger kids, and teachers aren't assigning difficult classics as much as they once did.

At Woodrow Wilson High School in Washington, D.C., the 11th-grade honors English students are reading The Kite Runner. And students like Megan Bell are reading some heavy-duty books in their spare time. "I like a lot of like old-fashioned historical dramas," Bell says. "Like I just read Anna Karenina ... I plowed through it, and it was a really good book."

But most teens are not forging their way through Russian literature, says Walter Dean Myers, who is currently serving as National Ambassador for Young People's Literature. A popular author of young-adult novels that are often set in the inner city, Myers wants his readers to see themselves in his books. But sometimes, he's surprised by his own fan mail.

"I'm glad they wrote," he says, "but it is not very heartening to see what they are reading as juniors and seniors." Asked what exactly is discouraging, Myers says that these juniors and seniors are reading books that he wrote with fifth- and sixth-graders in mind.

And a lot of the kids who like to read in their spare time are more likely to be reading the latest vampire novel than the classics, says Anita Silvey, author of 500 Great Books for Teens. Silvey teaches graduate students in a children's literature program, and at the beginning of the class, she asked her students — who grew up in the age of Harry Potter — about the books they like.

"Every single person in the class said, 'I don't like realism, I don't like historical fiction. What I like is fantasy, science fiction, horror and fairy tales.' "

Those anecdotal observations are reflected in a study of kids' reading habits by Renaissance Learning. For the fifth year in a row, the educational company used its Accelerated Reader program to track what kids are reading in grades one through 12.

"Last year, we had more than 8.6 million students from across the country who read a total of 283 million books," says Eric Stickney, the educational research director for Renaissance Learning. Students participate in the Accelerated Reader program through their schools. When they read a book, they take a brief comprehension quiz, and the book is then recorded in the system. The books are assigned a grade level based on vocabulary and sentence complexity.

And Stickney says that after the late part of middle school, students generally don't continue to increase the difficulty levels of the books they read.

Last year, almost all of the top 40 books read in grades nine through 12 were well below grade level. The most popular books, the three books in The Hunger Games series, were assessed to be at the fifth-grade level.

Last year, for the first time, Renaissance did a separate study to find out what books were being assigned to high school students. "The complexity of texts students are being assigned to read," Stickney says, "has declined by about three grade levels over the past 100 years. A century ago, students were being assigned books with the complexity of around the ninth- or 10th-grade level. But in 2012, the average was around the sixth-grade level."

Most of the assigned books are novels, like To Kill a Mockingbird, Of Mice and Men or Animal Farm. Students even read recent works like The Help and The Notebook. But in 1989, high school students were being assigned works by Sophocles, Shakespeare, Dickens, George Bernard Shaw, Emily Bronte and Edith Wharton.

Now, with the exception of Shakespeare, most classics have dropped off the list.

Back at Woodrow Wilson High School, at a 10th-grade English class — regular, not honors — students say they don't read much outside of school. But Tyler Jefferson and Adriel Miller are eager to talk. Adriel likes books about sports; Tyler likes history. Both say their teachers have assigned books they would not have chosen on their own. "I read The Odyssey, Tyler says. "I read Romeo and Juliet. I didn't read Hamlet. Asked what he thought of the books, Tyler acknowledges some challenges. "It was very different, because how the language was back then, the dialogue that they had.

Adriel agrees that books like that are tougher to read. "That's why we have great teachers that actually make us understand," he says. "It's a harder challenge of our brain, you know; it's a challenge."

But a challenge with its rewards, as Tyler says. "It gives us a new view on things."

Sandra Stotsky would be heartened to hear that. Professor emerita of education at the University of Arkansas, Stotsky firmly believes that high school students should be reading challenging fiction to get ready for the reading they'll do in college. "You wouldn't find words like 'malevolent,' 'malicious' or 'incorrigible' in science or history materials," she says, stressing the importance of literature. Stotsky says in the '60s and '70s, schools began introducing more accessible books in order to motivate kids to read. That trend has continued, and the result is that kids get stuck at a low level of reading.

"Kids were never pulled out of that particular mode in order to realize that in order to read more difficult works, you really have to work at it a little bit more," she says. "You've got to broaden your vocabulary. You may have to use a dictionary occasionally. You've got to do a lot more reading altogether."

"There's something wonderful about the language, the thinking, the intelligence of the classics," says Anita Silvey. She acknowledges that schools and parents may need to work a little harder to get kids to read the classics these days, but that doesn't mean kids shouldn't continue to read the popular contemporary novels they love. Both have value: "There's an emotional, psychological attraction to books for readers. And I think some of, particularly, these dark, dystopic novels that predict a future where in fact the teenager is going to have to find the answers, I think these are very compelling reads for these young people right now."

Reading leads to reading, says Silvey. It's when kids stop reading, or never get started in the first place, that there's no chance of ever getting them hooked on more complex books.

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